The invention relates to a roof support capable of being moved by its own drive mechanism whilst under permanent load.
In U.S. patent application Ser. No. 808,548, filed June 21, 1977 there is described a roof support which is capable of being moved by its own drive mechanism whilst under permanent load, the support comprising at least two parallel lower carriages which rest on the floor of a mine gallery, and which are connected together by two connecting cross-members, at least one upper carriage which bears against the roof of the gallery and is directed parallel to the lower carriages, and a jack which extends under pressure to force apart the connecting cross-members of the lower carriages and a support for the upper carriage. The carriages of a roof support of this kind may have articulated tracks, with or without rollers.
In the above-mentioned patent application the applicant described various modifications comprising four roof supports and having considerable flexibility because the beam of each of the four articulated track carriages is divided into longitudinal elements. There is also described an embodiment with a single prop but in which the carriages have rigid beams.
An object of the present invention is to provide a new roof support having a single prop, but in which the beams can nevertheless be divided into longitudinal elements, so that the roof support can adapt readily to irregularities of the height to be supported.
Another object of the invention is to provide a roof support in which the possible variation of height between the lowest position and the highest position of the upper part of the support is considerably increased.
Roof supports in which one or two upper carriages are carried by an arm articulated to the end of extensions of two lower carriages have already been proposed, particularly in French Pat. Nos. 1,503,990; 2,265,970; 2,265,971, 2,287,580, but these arrangements require two jacks, one per lower carriage. Furthermore, these prior supports have to be relieved of load before they can be advanced and cannot be adapted for operation under permanent load.
Finally, the lower carriage and the upper carriage are necessarily each in one piece and there is no articulation other than that between the lower carriages, so that the flexibility permitted by the roof support of the invention is impossible.
For practical reasons it was not possible to use lower carriages with articulated tracks with a known roof support in which the upper carriage is carried by an arm articulated to the end of the lower carriage, because the height of the carriages and the presence of articulated tracks make it impossible for the lower carriage to carry an extension or a jack. A new approach was therefore necessary which resulted in the invention.